Field of the Invention
The present invention relates to an image processing apparatus, a radiation imaging apparatus, control methods for them, a gain image creation method, a radiation imaging system, and a storage medium.
Description of the Related Art
Digital radiation imaging apparatuses and radiation imaging systems using these apparatuses have been commercialized. The digital radiation imaging apparatus irradiates an object with a radiation from a radiation irradiation source, and digitizes a radiation image serving as the intensity distribution of the radiation having passed through the object. Then, the apparatus performs necessary image processing on the digital radiation image, generating a clearer radiation image.
Recently, there are also implemented radiation imaging apparatuses and radiation imaging systems in which the radiation imaging apparatus itself can detect the start of irradiation with a radiation from a radiation generation apparatus to obviate the need for the connection between the radiation imaging apparatus and the radiation generation apparatus, and further improve installation, handling, and the like.
Japanese Patent Laid-Open Nos. 2011-247605 and 2011-249891 disclose methods of waiting for irradiation while sequentially selecting the respective scanning lines of a radiation imaging apparatus and switching the ON state/OFF state, and upon detecting a change of a current flowing inside the apparatus, detecting the start of irradiation with a radiation. According to this method, some of charges generated by irradiation with a radiation leak from a pixel corresponding to a scanning line on which scanning was stopped upon detecting the start of irradiation by the radiation imaging apparatus after the start of irradiation with the radiation. As a result, a linear or wedged defect may be generated in a radiation image.
Of processes from imaging to image obtainment, gain correction processing is generally performed on an obtained radiation image, in order to correct variations of the gains (sensitivities) of respective pixels arising from nonuniformity by the deposition process of a radiation detection sensor or the like, the presence of a singularly generated pixel with a different characteristic, aged deterioration or burn-in along with the use, or the like. In the gain correction processing, a radiation image (to be referred to as a gain image hereinafter) is used, which is obtained by uniformly irradiating the entire surface of the detection sensor with a radiation and imaging the surface at the time of installing a radiation imaging apparatus or periodically after installation. The output value of a radiation image obtained by irradiating an object with a radiation and imaging the object is divided by the output value of each corresponding pixel of the gain image.
However, when a gain image is sensed by the method of detecting the start of irradiation with a radiation from a change of an internal current, a linear or wedged defect is similarly generated even in the gain image. When the defect of the gain image is corrected by any image processing, a pixel in which the defect has been generated cannot correctly represent the original gain, and thus gain correction may not be performed correctly.
To solve the above problem, the present invention provides a technique for generating a defect-free sensitivity correction image even when irradiation with a radiation is detected based on a change of a current inside a radiation imaging apparatus and imaging is performed.